POS1418 ANTIGEN-SPECIFIC T-CELL DYNAMICS AND MULTIDIRECTIONAL IMMUNE DYSREGULATION IN SLE
Authors: G. A. Ramirez, E. Tassi, M. Noviello, B. A. Mazzi, L. Moroni, A. Sorce, L. Citterio, L. Zagato, E. Tombetti, E. Baldissera, G. Colombo, M. R. Yacoub, E. Bozzolo, C. Bonini, L. Dagna, A. Manfredi
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Systemic lupus erythematosus (SLE) is associated with autoimmune and allergic events along with impaired defensive responses. Dysregulated T-cell responses might account for this evidence but antigen-specific T-cell behaviour in SLE has not been characterised. <h3>Objectives</h3> To test for clinical/pathophysiological correlates of SLE immune dysfunction by characterising CD4+ T-cells selectively recognising key SLE-related, major histocompatibility complex (MHC)-restricted epitopes. <h3>Methods</h3> Human leukocyte antigen (HLA) DRB1*03:01 or 11:01-positive subjects were selected from a cohort of 222 patients with SLE and compared with patients with Takayasu's arteritis (TAK) and healthy controls (HC). <i>In silico</i> analyses through the Immune Epitope Database identified suitable HLA-peptide epitope pairs from a shortlist of autoantigens (histone H3 and H4), allergens (penicilloylated albumin) and pathogen-derived antigens (Epstein-Barr virus, EBV, nuclear antigens) based on the cohort clinical/serological profile. Fluorochrome-conjugated epitope-bound MHC tetramers were eventually built and used to detect antigen-specific CD4+ T-cells through flow cytometry. T-cell differentiation was assessed by CD45RA, CD62L and CD95 and polarisation by CD25, CD127, CD183, CD196 and CD194 staining. Epitope-specific reactivity was validated by multi-cytokine release assays and measurement of CD40L, CD137, OX40 and CD69 expression upon T-cell stimulation with the study peptides. SLE disease activity index 2000 (SLEDAI-2K) and lupus low disease activity state (LLDAS) were used to assess activity and remission. <h3>Results</h3> Total stem-cell memory T-cells (T<sub>SCM</sub>) were expanded in SLE compared to control groups. Histone-specific CD4+ T-cells were selectively found in SLE and clustered with anti-DNA antibodies. Only patients with beta-lactam allergy had anti-penicilloylated albumin T-cells. Anti-EBV-specific T cells were found in patients and controls (<b>Figure 1A-C</b>). Antigen-specific T-cell counts were reciprocally correlated. Histone-specific regulatory T-cells (Treg) were inversely correlated with SLEDAI-2K. Circulating histone- and EBV-specific effector memory T-cells (T<sub>EM</sub>) and Treg were lower in active SLE (<b>Figure 1D-F</b>). EBV-specific T<sub>SCM</sub> decreased in patients transitioning from remission to active SLE. Immunosuppressive treatment was associated with expanded CD4+ histone-specific T-cells. <i>In vitro</i> T-cell reactivity assays to study epitopes were consistent with <i>ex vivo</i> evidence. Higher IL17F and IL5 were released in response to histones and higher IL5 and IL22 in response to penicilloylated albumin-peptides in SLE. Defective anti-EBV IFNγ, TNF and IL22 release was observed in active SLE compared to HC. <h3>Conclusion</h3> Histone-specific T-cell responses constitute a hallmark of SLE and might defectively be regulated during active disease, promoting autoreactive effector peripheralisation into target tissues. Dysfunctional T-cell reactivity to EBV might also subtend a constitutional defect in the control of endogenous or exogenous viral stimuli and possibly contribute to autoreactivity through misdifferentiation of precursors. Aberrant responses to beta-lactam might also synergise with autoreactive responses and can accurately be detected through penicilloylated-albumin peptide T-cell reactivity. Antigen-specific (rather than total) T-cell dynamics might faithfully reflect the occurrence of key pathogenic events accounting for SLE immune dysfunction in response to multiple types of antigens and efficiently be used to track SLE phenotype heterogeneity. <h3>References</h3> [1]Abdirama D et al., Kidney Int, 2021 [2]Dolff S et al., Ann Rheum Dis, 2010 [3]Draborg AH et al. Lupus Sci &amp; Med, 2014 <h3>Acknowledgements</h3> Thanks to Dr Francesco Manfredi, Dr Rita El Khoury, Dr Laura Falcone, Dr Zulma Magnani, Prof. Patrizia Rovere-Querini Dr Eddie James and Prof. Bill Kwok for scientific counselling. We also thank Dr. Valeria Beretta, Dr Elisa Cantarelli, Dr Annalisa Capobianco, Dr Michela Grossi, Dr Francesco Manfredi, Dr Norma Maugeri, Dr Elisabetta Messaggio, Dr Antonella Monno, Dr Clara Sciorati, Dr Serenesse Tomasi, Dr Cristina Tresoldi and Dr Veronica Valtolina, Dr. Valentina Canti and Dr. Rebecca De Lorenzo. <h3>Disclosure of Interests</h3> Giuseppe Alvise Ramirez Consultant of: Astrazeneca, Elena Tassi: None declared, Maddalena Noviello: None declared, Benedetta Allegra Mazzi: None declared, Luca Moroni Consultant of: Astrazeneca, Andrea Sorce: None declared, Lorena Citterio: None declared, Laura Zagato: None declared, Enrico Tombetti: None declared, Elena Baldissera: None declared, Giselda Colombo: None declared, Mona-Rita Yacoub: None declared, Enrica Bozzolo: None declared, Chiara Bonini: None declared, Lorenzo Dagna Consultant of: Abbvie, Amgen, Astra-Zeneca, Biogen, Boehringer-Ingelheim, Bristol-Myers Squibb, Celltrion, Eli Lilly and Company, Galapagos, GlaxoSmithKline, Janssen, Kiniksa Pharmaceuticals, Novartis, Pfizer, Roche, Sanofi-Genzyme, Swedish Orphan Biovitrium (SOBI), and Takeda, Grant/research support from: Abbvie, Bristol-Myers Squibb, Celgene, GlaxoSmithKline, Janssen, Kiniksa, Merk Sharp &amp; Dohme, Mundipharma Pharmaceuticals, Novartis, Pfizer, Roche, Sanofi-Genzyme, and SOBI., Angelo Manfredi: None declared.